1. Field of the Invention
The present invention relates to a control of an industrial robot and more particularly to a control of a working robot which holds a work to bring it against a tool to be worked by the tool.
2. Description of the Prior Art
Known industrial robot technology includes a working robot which is adapted to hold a workpiece and bring it to a position where it is placed against a tool to be worked by the tool. The tool may be of any kind, such as a torch of an arc welding equipment, a spray nozzle of a painting equipment or a spray nozzle of a sealant applying equipment. The robot includes an arm mechanism having a hand which can be moved about a plurality of axes. The workpiece is gripped by the hand and moved with respect to the tool so that the tool traces a predetermined path on the workpiece. Prior to the actual work being performed, a teaching is made so that the robot is located against the tool at predetermined positions and predetermined orientations in a plurality of teaching points on the predetermined path.
The robot must be controlled so that the workpiece can be moved with respect to the tool smoothly from the predetermined position and the predetermined orientation at one teaching point to those at another teaching point. For the purpose, an incremental compensation control is made between each two adjacent teaching points. The position of the tool with respect to the workpiece can be represented in terms of the distance between a point on the robot hand and the working end of the tool as measured in the direction of the axis of the tool and the distance is generally referred as the "tool length". The orientation of the tool with respect to the workpiece can be represented in terms of the direction of the axis of the tool and the tool length having the directionality along the axis of the tool may be referred as the "tool length vector". Conventionally, the control unit for the robot has a memory storing a plurality of different values for the tool length vector and closest ones are selectively used at each teaching point, the compensation control being carried out depending on the selected values of the tool length vector in each teaching point.
According to the conventional manner of compensation control, deviations are always produced from desired values in respect of the tool length vector at any point between each two adjacent teaching points. In order to make the deviations as small as possible, it is necessary to increase the number of values to be stored in the memory. Alternatively, the number of the teaching points may be increased so that the distance between each two adjacent teaching points can be decreased. However, either of the solutions are not preferable because it requires increased labor and time for the teaching.